Lung cancer presents most frequent neoplasms in American males. Small cell carcinoma of the lung, a highly lethal cell type, has recently been described as having a consistent deletion of the short arm of chromosome 3(p14-23). Identification of the genetic material consistently lost may lead to greater understanding of the pathogenesis of small cell carcinoma of the lung and may perhaps aid in the development of rational schemes for treatment and prevention. This research focuses on identification of cell surface antigens expressed in rodent human somatic cell hybrids using monoclonal antibody techniques, to investigate the following questions. (1)\What cell surface antigens are encoded by chromosome 3? (2)\What cell surface antigens are expressed by the deleted segment of chromosome 3 lost in small cell carcinoma? (3)\What cell surface antigens are expressed by small cell carcinoma? (4)\What cell surface antigens are expressed by normal cells, but not by small cell carcinoma? (5)\Are any cell surface antigens unique to small cell carcinoma? By understanding the genetic abnormality in this common malignancy, we hope to gain greater insight into its initiation, pathogenesis, diagnosis and treatment.